Shiwei Long

Thermochromic multilayer films of WO3/VO2/WO3 sandwich structure with enhanced luminous transmittance and durability

A novel thermochromic WO3/VO2/WO3 sandwich structure was deliberately designed and deposited by a reactive magnetron sputtering technique. The double layer of WO3 not only functions as an antireflection (AR) layer to enhance the luminous transmittance (Tlum) of VO2, but also performs as a good protective layer for thermochromic VO2. Basically, the bottom WO3 layer functions as a buffer beneficial for the formation of the intermediate VO2 layer and serves as an AR layer while the intermediate VO2 layer with primary monoclinic phase acts as an automatic solar/heat control for energy saving. The top WO3 layer acts as another AR layer, and provides protection in a complex environment. An obvious increase in Tlum by 49% (from 37.2% to 55.4%) is found for VO2 films after introducing double-layer WO3 AR coating. The VO2 deposited on glass exhibits good thermochromism with an optical transition at 54.5 °C, which decreases to 52 °C in WO3/VO2/WO3 sandwich structure, and the hysteresis loop is sharper around the transition temperature, which may be ascribed to the strain and interfacial diffusion. In comparison with single-layer VO2, the durability in automatic solar/heat control of sandwich-structure VO2 films is improved nearly 4 times in high temperature and humidity conditions. This multilayer will open a new avenue for the design and integration of advanced thermochromic heterostructures with controllable functionalities for intelligent window and sensing system applications.

Structure and enhanced thermochromic performance of low-temperature fabricated VO2/V2O3 thin film

For VO2-based smart window manufacture, it is a long-standing demand for high-quality thin films deposited at low temperature. Here, the thermochromic films of VO2 were deposited by a magnetron sputtering method at a fairly low temperature of 250 °C without subsequent annealing by embedding a V2O3 interlayer. V2O3 acts as a seed layer to lower the depositing temperature and buffer layer to epitaxial grow VO2 film. The VO2/V2O3 films display high solar modulating ability and narrow hysteresis loop. Our data can serve as a promising point for industrial production with high degree of crystallinity at a low temperature.

Optical and electrical performance of thermochromic V2O3 thin film fabricated by magnetron sputtering

V2O3 was recognized as one of the clearest examples of Mott-Hubbard physics but was rarely treated as transmittance modulating coatings based on the metal-insulator transition. Here, we deposited high quality epitaxial V2O3 thin films on sapphire (001) substrates as well as polycrystalline V2O3 films on glass or Si substrates, measured the optical properties during cooling and heating, and discussed the modulating ability using fully reversible optical hysteresis loops. Meanwhile, we also optimized the electrical performance of V2O3/SiNx/Si samples by W-Ti co-doping. The obtained co-doped V2O3 film shows a relatively high temperature coefficient resistance of −8.1%/K at 80 K without hysteresis loops, which exhibits great potential in high sensitivity thermal resistor devices. Our work provides a comprehensive scenario of the V2O3 thin film physics.

Facile and Low-Temperature Fabrication of Thermochromic Cr2O3/VO2 Smart Coatings: Enhanced Solar Modulation Ability, High Luminous Transmittance and UV-Shielding Function

In the pursuit of energy efficient materials, vanadium dioxide (VO2) based smart coatings have gained much attention in recent years. For smart window applications, VO2 thin films should be fabricated at low temperature to reduce the cost in commercial fabrication and solve compatibility problems. Meanwhile, thermochromic performance with high luminous transmittance and solar modulation ability, as well as effective UV shielding function has become the most important developing strategy for ideal smart windows. In this work, facile Cr2O3/VO2 bilayer coatings on quartz glasses were designed and fabricated by magnetron sputtering at low temperatures ranging from 250 to 350 °C as compared with typical high growth temperatures (>450 °C). The bottom Cr2O3 layer not only provides a structural template for the growth of VO2 (R), but also serves as an antireflection layer for improving the luminous transmittance. It was found that the deposition of Cr2O3 layer resulted in a dramatic enhancement of the solar modulation ability (56.4%) and improvement of luminous transmittance (26.4%) when compared to single-layer VO2 coating. According to optical measurements, the Cr2O3/VO2 bilayer structure exhibits excellent optical performances with an enhanced solar modulation ability (ΔTsol = 12.2%) and a high luminous transmittance (Tlum,lt = 46.0%), which makes a good balance between ΔTsol and Tlum for smart windows applications. As for UV-shielding properties, more than 95.8% UV radiation (250-400 nm) can be blocked out by the Cr2O3/VO2 structure. In addition, the visualized energy-efficient effect was modeled by heating a beaker of water using infrared imaging method with/without a Cr2O3/VO2 coating glass.

Multi-nanolayered VO 2 /Sapphire Thin Film via Spinodal Decomposition

Coating of VO2-based thin film has been extensively studied for fabricating energy-saving smart windows. One of the most efficient ways for fabricating high performance films is to create multi-nanolayered structure. However, it has been highly challenge to make such layers in the VO2-based films using conventional methods. In this work, a facile two-step approach is established to fabricate multilayered VO2-TiO2 thin films. We first deposited the amorphous thin films upon sputtering, and then anneal them to transform the amorphous phase into alternating Ti- and V-rich multilayered nanostructure via a spinodal decomposition mechanism. In particular, we take advantage of different sapphire substrate planes (A-plane (11–20), R-plane (1–102), C-plane (0001), and M-plane (10-10)) to achieve different decomposition modes. The new approach has made it possible to tailoring the microstructure of the thin films for optimized performances by controlling the disorder-order transition in terms of both kinetic and thermodynamic aspects. The derived thin films exhibit superior optical modulation upon phase transition, significantly reduced transition temperature and hysteresis loop width, and high degradation resistance, these improvements indicate a high potential to be used for fabricating the next generation of energy saving smart windows.